Default [Q] How to change permission in system file Android

Hi to everyone,
I try to make a cpu control app for android devices.
I have stuck and i want to ask you how can i change the clock frequency with java.
I think that i have to change the frequency in this file /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq in order to change the max frequency. So i want to ask you how can i change the file permission?